A French policeman has been shot dead and two others wounded in central Paris in an attack carried out days before presidential elections and quickly claimed by the Islamic State militant group.

Key points:

Police targeted in attack but motive still unknown, French authorities say

Attacker's identity yet to be established, police say

Interior Ministry says a "weapon of war" was used against police

Paris police spokeswoman Johanna Primevert said the attacker targeted police guarding the area near the Franklin D Roosevelt metro stop on the Champs Elysees on Thursday night (local time) at the centre of the avenue, which is popular with tourists.

One witness was walking on the pavement nearby when the gunman appeared.